JPH0328689B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a processing method for a focus detection method used in an optical device such as a camera.

2. Description of the Related Art As one method of a focus detection device for a conventional camera, a method is known in which the pupil of a photographing lens is divided and the shift of two images formed is observed to determine the in-focus state. For example, US Pat. No. 4,185,191 discloses a device in which a fly-eye lens group is arranged on the intended image formation plane of a camera lens and generates two images shifted in accordance with the amount of defocus of the camera lens.
In addition, so-called secondary imaging is performed in which the aerial image formed in the planned image is guided to the solid-state image sensor surface by two secondary imaging systems arranged in parallel, and the relative positional shift of each image is detected. The method is disclosed in Japanese Patent Application Laid-open No. 55-118019, Japanese Patent Application Laid-open No. 55-155331, etc. The latter secondary imaging method has the advantage that it does not require a special optical system, although the overall length becomes slightly larger.

The principle of this secondary imaging type focus detection device is explained first.
To explain briefly using a diagram, the field lens 2 has the same optical axis as the photographic lens 1 that performs focus detection.
are arranged, two secondary imaging lenses 3a and 3b are arranged in parallel behind these lenses, and light receiving sensor arrays 4a and 4b are arranged further behind them, respectively. Note that 5a and 5b are apertures provided near the secondary imaging lens. The field lens 2 connects the exit pupil of the photographing lens 1 with two secondary imaging lenses 3.
The images are approximately formed on the pupil planes a and 3b. As a result,
The light beams incident on each of the secondary imaging lenses 3a and 3b are distributed over areas of equal area that do not overlap with each other and correspond to the respective secondary imaging lenses 3a and 3b on the exit pupil plane of the photographing lens 1. It will be ejected from. When the aerial image formed near the field lens 2 is re-imaged onto the surfaces of the sensor arrays 4a and 4b by the secondary imaging lenses 3a and 3b,
Based on the difference in the positions in the optical axis direction where the aerial images were formed, the two re-formed images change their positions. FIG. 2 shows how this development occurs, with the sensor arrays 4a and 4b centered on the in-focus state shown in FIG. The two images formed on the surface move in opposite directions on the sensor array 4a, 4b surface. The in-focus state can be determined by photoelectrically converting this image intensity distribution and detecting a relative positional shift between the two images using an electrical processing circuit.

Methods for processing photoelectrically converted signals are known, for example, in Japanese Patent Laid-Open No. 54-87222 and US Pat. No. 4,250,376. The received light signals obtained by photoelectrically converting the two secondary images are a(i), b(i), respectively (where i
= 1 to N), in the known example, for an appropriate constant k, V= _NK 〓 ⁱ⁼¹ |a(i)−b(i+k)|− _NK 〓 ⁱ⁼¹ |a(i+k)− b(i)|...(1) is calculated by an analog calculation circuit or digitally, and the direction in which the photographing lens 1 is extended is determined based on the sign or negative of this value of V. In this case, the value of k is usually chosen to be k=1. In FIG. 3, A and B specifically show the light intensity distributions of two images to be photoelectrically converted whose positions have changed relative to each other. Here 41 and 4
The set of points 1', 42 and 42' etc. is the sensor array 4.
It represents the output of the corresponding element pair a, 4b. For example, when k = 1, the first term of equation (1) is 41
and 42', 42 and 43', etc., and their absolute values are added. Therefore, this signal processing method uses the characteristics A and B obtained from the two images.
This is nothing but finding the area of the difference between them and determining in which direction of the lens extension position this area is concentrated.

However, the above-mentioned calculation requires the determination of an absolute value, which has the disadvantage that the electrical circuit for realizing this is complicated. Furthermore, since the outputs of each pair of elements are subtracted, errors in each output value are accumulated, which poses a problem in the accuracy of the calculation.

An object of the present invention is to provide a focus detection method using a novel signal processing method that is simpler and more accurate than conventional methods in a focus detection device that forms two images using a pupil division method. The gist of this method is to divide the pupil of the main imaging optical system to be focus-detected, and use a photoelectric conversion element array to generate multiple object images formed by the imaging light beams emitted from each divided pupil area. When determining the in-focus state by electrical detection, a plurality of photoelectric conversion element arrays that receive the respective object images are made to correspond in a certain correspondence relationship, and the photoelectric outputs of the corresponding elements are respectively The feature is that a focus state determination signal is obtained by performing arithmetic processing of comparing, extracting and adding the minimum or maximum output values.

The present invention will be explained in detail based on illustrated embodiments.

First, as an example of the present invention, V= _NK 〓 ⁱ⁼¹ min{a(i), b(i+k)}− _NK 〓 ⁱ⁼¹ min{a(i+k), b(i)}...(2) A focus detection method for calculating the focus state determination signal V will be described below. In equation (2), the photoelectric output nozzle signals a(i), b(i), (where i = 1 to N) are all positive value signals, and min{x, y} are two positive real numbers x, The smaller value of y is shown. Characteristics A and B in FIG. 3 above are two secondary images, namely a
(i), b(i), (i = 1 to N) respectively, and the output signals are from 41, 41' to 5 in the same figure.
Up to 4,54'. Here, if the output signal at point 41 is expressed as A (41), the output signal at point 41' is expressed as B (41'), etc., then the first term V ₁ of equation (2) is expressed as V ₁ = min {A (41),B(42')}+min{A
(42), B(43')} +min{A(43), B(44')}+...
+min {A(53), B(54')}...(3), and applying it specifically to the output signal in the same figure, V ₁ = B(42') + B(43') +...+A(52 ) + A (53) ...(4). Similarly, finding the second term V ₂ in equation (2), we get
V=V ₁ -V ₂ is positive in FIG. 3, indicating that the lens is not in focus. Each term in equation (2) above has characteristics A,
A common surrounded area is obtained while B is slightly shifted from each other, and the smaller V becomes, the closer to the in-focus state it becomes. After performing this operation, V
By driving the photographing lens 1 in a predetermined direction depending on the sign of the image, it is possible to bring the lens 1 closer to the in-focus state. When in focus, V=O should be achieved,
Practically speaking, a focus determination reference width ε may be set, and in-focus may be determined when the absolute value of V is smaller than ε. FIG. 4 shows how the above-mentioned value of V changes depending on the extended position of the photographic lens 1.

FIG. 5 shows an example in which this calculation is performed using an analog calculation circuit. Reference numerals 61 and 62 are sensor arrays that receive secondary images, and the light reception signals output from these as time-series signals are sent to a two-stage analog circuit. It passes through the system registers 63 and 64. sensor array 6
Sensor arrays 1 and 62 do not need to be physically separated into two lines and may be used by partially dividing one line of sensor arrays. These electronic components are synchronously controlled by a clock generating circuit (not shown).
The shift registers 63 and 64 are a(i) and a, respectively.
A comparator 65 holds the signals of (i+1), b(i), b(i+1) and determines the two equations min{a(i), b(i+1)}, min{a(i+1), b (i)}
It is connected to a comparator 66 that determines.
Comparator 65 and its inverted output
NOT gate 71 is exclusively connected to analog switch 6
7 and 68, and the integrator 73 has min{a(i), b
(i+1)} is output. Similarly, comparator 66
and its inverted output gate 72 exclusively controls the analog switches 69 and 70, and the integrator 74
Output {a(i+1), b(i)}. Integrator 73,
The output of 74 is led to a differential amplifier 75, which outputs a focus state determination signal V.

The focus detection processing circuit shown in FIG. 5 does not require any nonlinear arithmetic processing such as multiplication, division, or absolute value, so it can be easily realized with an analog arithmetic circuit. Of course, the use of digital arithmetic circuits also has the great advantage of not requiring nonlinear processing.

Next, another embodiment of the present invention will be described. In this example, V= _NK 〓 ⁱ⁼¹ max{a(i), b(i+1)}− _NK 〓 ⁱ⁼¹ max{a(i+k), b(i)}...(5) calculate. However, max{x, y} indicates the larger of the two positive real numbers x, y, and the other signals are the same as those described in the previous embodiment. While the previous example selected the smallest of characteristics A and B and found the area area commonly surrounded by both characteristics, this example selects the area area that includes both characteristics A and B. Performing extraction calculations. When this arithmetic expression (5) is used, the sign of the value of the focus state determination signal V for the extended position of the photographic lens is reversed compared to the previous embodiment. Therefore, the driving direction of the photographing lens, which is predetermined by the positive or negative value of V, is opposite to that of the previous embodiment. In terms of the circuit, in the above-mentioned FIG. 5, arithmetic processing is performed by switching the connections between the outputs of the comparators 65 and 66 and the NOT gates 71 and 72 that produce their inverted outputs, and the analog switches 67, 68, 69, and 70. is realized.

As described in detail above, the focus detection method according to the present invention does not require calculating the difference in characteristics obtained from two sensor arrays as in the conventional example, and does not require nonlinear calculation processing. Therefore, the interference of errors is small and the circuit for realizing calculations does not become complicated. Therefore, by using this method, a pupil division type focus detection device can be constructed simply and with high precision.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of the principle of a focus detection device using a secondary imaging method, Fig. 2 a, b, and c are explanatory diagrams of the principle of image shift, and Fig. 3 is an illustration of the principle of image shift. Output characteristic diagram of the secondary image, Figure 4 is an explanatory diagram of the focusing signal,
FIG. 5 is a circuit configuration diagram of an embodiment for realizing the method of the present invention. Code 1 is a photographic lens, 2 is a field lens,
3a and 3b are secondary imaging lenses, and 4a and 4b are sensor arrays.

Claims (1)

[Claims] 1. Divide the pupil of the main imaging optical system whose focus is to be detected, and electrically detect multiple object images formed by the imaging light flux emitted from each divided pupil area using a photoelectric conversion element array. When determining the in-focus state by determining the in-focus state, a plurality of photoelectric conversion element arrays that receive the respective object images are made to correspond according to a certain correspondence relationship, and the photoelectric outputs of the corresponding elements are compared, and the minimum Alternatively, a focus detection method is characterized in that a focus state determination signal is obtained by performing arithmetic processing to extract and add maximum output values.